One type of defect typically encountered in the manufacture of resin-impregnated articles produced by resin transfer molding, such as fan blades, propeller blades and other types of aircraft components, is the occurrence of resin-depleted areas or "dry spots". In a typical resin transfer molding process, a liquid resin is injected into an evacuated mold cavity containing a structural preform of the article. The structural preform is typically made of fibers, such as fiberglass, carbon, graphite and KERLAR.TM., braided or woven into sheet form, with the sheets being laid on top of one another forming a laminated preform. The fiber preform absorbs the liquid resin as it is injected under pressure into the evacuated cavity, and once the preform is saturated and impregnated with resin, it is thermally cured to form the article. If the resin is not fully absorbed, or otherwise fails to fully infiltrate the preform, one or more dry spots may result in the "resin starved" areas, rendering the article defective. These dry spots can be caused, for example, by an insufficient vacuum within the mold cavity, excessive moisture in the mold cavity, excessive fiber content in the preform, or a blockage or other interruption in a resin line leading to the mold cavity. Dry spots or like voids are particularly unacceptable in aircraft components, such as propeller or fan blades, because they can significantly degrade the structural integrity of the component.
According to one known method for repairing dry spots, the resin-depleted area of the preform is first removed using, for example, a knife or similar tool. Then, the lamination immediately surrounding the dry spot is scarfed forming a recess or cavity in the surface of the article slightly larger than was the dry spot. Typically, an area of about 1/4 inch wide surrounding the dry spot is scarfed for each lamination forming a part of the respective dry spot. A thin coating of resin is then brushed over the entire scarfed surface and is cured to seal the recess. Patch plies are also cut from the same type of sheet material used to make the preform, and the orientation of the fibers is selected to match that of the material removed. The resin-sealed surface of the scarfed recess is then lightly abraded and cleaned, and the patch plies are wet with resin and placed in proper position over the sealed surface. A vacuum bag is then placed over the patch plies and is evacuated in order to draw excess resin from the patch. Once the resin is cured, the vacuum bag is removed, and the patch is abraded or sanded in order to blend the patched surfaces with the surrounding contour of the article.
One drawback of this method of repair is that it is extremely time consuming, and requires skilled and intensive labor, and thus is relatively expensive. Also, the patched area is typically considerably weaker, at times on the order of 15% weaker, than the base lamination.
It is an object of the present invention to overcome the drawbacks and disadvantages of prior art methods and systems for repairing defective articles produced by resin transfer molding.